Cutting tools are used to remove metal as chips from a metal workpiece. Such tools have evolved into many specialized shapes but universally comprise a cutting edge which is urged into moving contact with the workpiece for removal of metal in shaping the workpiece. In the automobile industry, for example, cast silicon-containing aluminum alloys are used to form engine blocks and metal is cut from the cast surfaces, using cutting tools such as drills, boring bars and face mills, to give shape to the engine block.
Tool cutting edges are subjected to high loading and high temperatures as well as mechanical and thermal shock. This difficult environment leads to degradation of the cutting edge due to either wear or fracture. When the edge degradation reaches unacceptable levels the cutting process must be interrupted and the tool must be replaced or re-sharpened, which has prompted continuing investigations into new or improved cutting tool materials in an effort to prolong useful tool life. Currently, carbide tools generally comprising hard particles of tungsten carbide held in a metal matrix, usually cobalt, are the preferred tools for general purpose metal machining. Sometimes nickel and/or chromium are used in the metal matrix binder. The metal matrix typically makes up about five to ten percent by volume of the tungsten carbide plus matrix volume. Carbide particles sizes often range from about 1.5 to about ten micrometers in largest dimension (sometimes classified as from fine to medium).
However carbide tools are challenged by machining the aluminum-silicon engine alloys used by the automobile industry since the hard silicon particles in the alloy promote rapid tool wear. One approach to reducing the wear rate is to apply a hard, wear-resistant surface coating to the carbide tool, and for this application, diamond coatings have been preferred. Diamond however is a ceramic and therefore intrinsically brittle and prone to chipping. Also, achieving good adhesion between the diamond coating and the carbide tool can be difficult. Thus there is a need for a process to deposit an improved, adherent, tough diamond or diamond-containing coating on carbide tools.